Deeply Embedded Protostellar Population in the Central Molecular Zone Suggested by H$_2$O Masers and Dense Cores

TL;DR

This study investigates star formation in the Central Molecular Zone's massive clouds using high-resolution radio and millimeter observations, revealing deeply embedded protostellar candidates and dense cores, with some clouds showing signs of early star formation activity.

Contribution

First detailed high-resolution survey of embedded star formation in CMZ clouds, identifying new protostellar candidates and dense cores in extreme galactic environments.

Findings

Detection of new deeply embedded protostellar candidates.

Identification of dense cores associated with water masers.

Some clouds remain quiescent with no signs of active star formation.

Abstract

The Central Molecular Zone (CMZ), usually referring to the inner 500 pc of the Galaxy, contains a dozen of massive ($\sim10^5$ $M_\odot$) molecular clouds. Are these clouds going to actively form stars like Sgr B2? How are they affected by the extreme physical conditions in the CMZ, such as strong turbulence? Here we present a first step towards answering these questions. Using high-sensitivity, high angular resolution radio and (sub)millimeter observations, we studied deeply embedded star formation in six massive clouds in the CMZ, including the 20 and 50 km s$^{-1}$ clouds, Sgr B1 off (as known as dust ridge clouds e/f), Sgr C, Sgr D, and G0.253-0.016. The VLA water maser observations suggest a population of deeply embedded protostellar candidates, many of which are new detections. The SMA 1.3 mm continuum observations reveal peaks in dust emission associated with the masers, suggesting the existence of dense cores. While our findings confirm that clouds such as G0.253-0.016 lack internal compact substructures and are quiescent in terms of star formation, two clouds (the 20 km s$^{-1}$ cloud and Sgr C) stand out with clusters of water masers with associated dense cores which may suggest a population of deeply embedded protostars at early evolutionary phases. Follow-up observations with VLA and ALMA are necessary to confirm their protostellar nature.